Control mechanism



1966 H. CATLING ETAL 3,231,940

CONTROL MECHANISM Filed March 15, 1962 INVENTORS: HAROLD CH 7'1. ING- Lu w YN DA was United States Patent 3,231,940 I CONTROL MECHANISM Harold Catling and Islwyn Davies,'Manchester,-z England, assignors to, The Cotton Silk and Man-Made Fibres Research Association, a British association of Great Britain, Northern Ireland, and the Isle of Man Filed Mar. 13, 1962, Ser. No. 179,319 Claims priority, application Great Britain, Mar. 15, 1 961, 9,396/ 61 3-Claims. (Cl. 19--97.5)

This invention concerns control mechanisms ofthe type having means sensitive to the value of some property (such as the thickness) of a travelling material, said means being adapted, on sensing deviations of said value from a desired value, to adjust'the action of further means, which operates to influence the value of the property, compensatively. The real purpose of such mechanisms may be to control the value of a certain property other than that actually sensed by said first-mentioned means, on the assumption that there is a consistent proportional relationship between the value of the certain property to be controlled and the value of the property actually sensed. For example, where the thickness of a web of travelling fibrous material is the property being sensed the weight per unit length of the material may be the certain property which it is the essential object tocontrol. The present invention is concerned exclusively with control mechanisms in which the sensing means operates indirectly in this'manner (hereinafter referred to as control mechanisms of the type referred to).

' In control mechanisms of the type referred to it may be that certain changes can occur which render the assumption on which the indirect operation is based no longer valid. Thus, for example, important factors which may influence the thickness-weight per unit length relationship of a fibrous web passing. through a scutcher are the moisture content of the web, the air permeability of the web, the size of the tufts of fibres which form the web, and the temperature of'the web. The object of the present invention is to provide a control mechanism of the type referred to which is improved in so far as its indirect mode of operations is concerned, in that such changes can be taken into account.

According to the present invention a control mechanism of the type described incorporates additional means" sensitive to change in a property (such as moisture con-' tent of the traveling material) affecting the proportionality on which thesatisfactory indirect operation of the mechanism depends, and adapted, on detecting such change, so to modify the characteristics 'ofthe mechanism that the latter operates as if said proportionality were undisturbed. The change may be in at least one property of the material. This is preferably done by designing the additional means so that it changes an operational reference level of the controlmechanism to a degree dependent upon the amount of said change and the nature of its affect on said proportionality.

I: The principles involved in the invention are best illustrated by way of a practical example of its application; which will now be described. l i In co-pending application 844,425, now US. Patent No.' 3,109,204, is described a control mechanism of the type referred to as used on a scutcher, a well-known de-.

vice for modifying the characteristics ofa traveling mass;

of textile fibres and the accompanying drawingflshows diagrammatically a scutcher incorporating that control mechanism in a form which is improved in accordance with the present invention. i

Basically the control mechanism before improvement consists of an open loop part which operates to alter:

, spect to time from a desired thickness detected at the calender rollers. The function of the control mechanism is to maintain the weight per unit length of the material substantially constant, and its satisfactory operation is based on the consistency of a given linear relationship between the thickness of the material and its weight per unit length. Unfortunately, the material may be sub jected to a number of variable factors any one of which alters this relationship. One such factor which is usually of importance is the amount of moisture contained therein. In accordance with the invention, therefore,-

' additional means are provided, in association with the closed loop part of the control mechanism to detect changes in the moisture content of the material and to alter the reference level of the closed loop part of the; control mechanism in such a way that the mechanism. still functions satisfactorily.

Referring now to the figure, the main parts of the scutcher comprise the beater 11, the top cage 12, the, bottom cage 13, the calender rollers 14, 15, 16, 17, and. the lap rollers 18, 19. Cotton is fed to the beater 11 by a feed lattice 20 and via a pedal roller 21 operatively associated with a pedal assembly 22 supported by a knifev rail 23.

'I'he pedal assembly 22 is connected by a link motion 24 to a lever 25 which is itself pivoted to a nut 26. One end of the lever 25 carries a counter-weight 27 whilst the other end carries a link 28'for operating the plunger 29 of a valve 30. The valve forms part of a control circuit for a variable speed hydraulic motor 31, the other main elements of the circuit being a pump 32, and a tank 33 for hydraulic fluid. -The motor 31 drives the. pedal roller 21 through a worm 34 and worm-wheel 35. Above the top calendar roll 14 is disposed a detector. system 36, including a transducer 36a sensitive to the vertical position of the roll 14 and adapted, by means ofan electro-mechanical system 37 to rotate a shaft 38'.

carrying a worm 39 in mesh with a worm-wheel 40. The; electro-mechanica-l system 37 consists of an' amplifier. arrangement 37a, a servo-motor 37b, and a gear-box. 370, with a feed back 3741. The worm-wheel 40 is di-. rectly supported by an axially fixed lead-screw 41 on which the nut 26 is engaged.

The control device, theparts of which have, with ref-i erence to the figure, just been described, is designed 'so' that as cotton 42 is fed to' and passes through "the in the rate of feed of cottonremaining constant- (assum- 11 weight. per

ing the relationship between thickness and unit area to be unchanged).

the lap passing through the calender roll system, and is arranged to cause through associated control means, movement of. the lead-screw 41 in response to long-term fluctuationsof the thickness of the material. Thus'when there is for example a slow increase in the mean thick- I The detector system 36 is sensitive to the thickness bri;

ness of the cotton at the calender rolls the lead-screw 41 turns in such sense as to displace the nut 26 and thus the pivot point of lever in a direction which causes the system for correcting short-term fluctuations to operate about a different datumcorresponding to a slower motor speed. Thus, there is an adjustment of the, open loop control system which'at any time is proportional to the integrated deviation of thickness with respect to time from a desired value.

In this manner both short-term and long-term fluctuations are dealt with (except, of course short-term fluctuations which arise after the pedal roller).

' Thus far the control mechanism is that already described in co-pending application 844,425, now US. Patent No. 3,109,204, and the additional means will now be described whereby the mechanisms are made selfcompensating for variations in moisture content of the material being processed.

- The transducer 36a is mounted in a bar 43 pivotally mounted at one end and supported by a screw device at the other end. This device consists of a lead-screw 44 axially movable in a fixed threaded housing 44a by virtue of the drive from a servo motor 45 transmitted through a worm 46 and worm-wheel 47, the latter being connected to the lead-screw 44. The lead-screw 44 also carries a micrometer nut 48 for setting purposes.

The servo-motor 45 is under the control of a special electrical circuit whereby differences in moisture content of the material passing between the calender rollers 14, 15, 16 are detected and the speed and direction of rotation of the servo-motor 45 controlled accordingly and in such manner that adjustment of the bar 43 and therefore transducer 36a takes place. The arrangement is such that these adjustments compensate for changes in the thickness-weight per unit length relationship due to changes in the moisture content of the material.

The electrical circuit consists basically of a conventional bridge ABCD. A voltage supply is connected across AC, and AB and BC are suitable resistors. Point C is grounded and point D is connected to ground via the surface portion of calender roller 15 isolated by a band 15a of insulated material, the material passing therearound and rollers 14, 16, this connection therefore constituting the arm CD of the bridge. Between A and D is connected a special non-linear variable resistor 49, the movable contact 50 of which is carired by a nut 51 mounted on a lead-screw 52 on one extended end of the shaft of the servo motor 45. An amplifier 53 is connected across DB, the output signal from which is adapted to control the direction and speed of rotation of the servo motor 45.

The arm CD of the bridge circuit detects change of moisture content as reflected in a change of electrical resistance, and the rate of movement of the contact 50 of the variable non-linear resistor 49, and the non-linearity of the latter, are arranged so that the ohmic value of the arm AD is adjusted according to the particular relationship between thickness, weight per unit length and moisture content of the material being processed.

- In operation, with the moisture content of the material at the datum level, and therefore a given proportionality between thickness and weight per unit length of the material the control mechanism functions normally as disclosed in co-pending application aforesaid. Should however, the moisture content of the material decrease, say, the thickness-weight per unit length relationship of the material will change and without the additional means provided in accordance with the present invention the control mechanism would begin to react as though the weight per unit length had become increased (due to the increase in thickness) when in fact there would have been no such change. However, the additional means described above will come into operation as soon as such a. change commences. Before the change commences the bridge circuit will be balanced and no signal will be coming from the amplifier, the servo motor 45 being therefore stationary. As the moisture content begins to drop this will affect the ohmic value of arm CD and the resultant signal from the amplifier will start to rotate the servo motor 45. The speed of rotation will be proportional to the voltage between B and D and the direction of rotation will be such as to cause the lead screw 44 to raise the arm 43 slightly so that, in spite of the increase in thickness of the material, no increase in thickness is signalled by the electro-mechanical system 37. At the same time the nut 51 and contact 50 are moved by the rotation of the servo motor shaft 52 so as to alter the ohmic value of arm AD to bring the bridge into balance again so that the servo motor '45 ceases to rotate. 011 increase of moisture content the action is reversed. It is to be noted that it is immaterial whether the open loop part of the control mechanism is affected or not by the change of moisture content.

It may be mentioned that slight variations in electrical resistance of the lap occur due to changes in thickness of the lap. However, these variations are extremely small compared to the variations in resistance due to changes in moisture content of the lap. In part, this is a result of the fact that large variations in thickness of the lap to not occur in practice. Thus, any error, such as slight over correction for the influence of moisture, which may be introduced by variations in lap thickness are as a practical matter negligible.

The preceding description and associated drawing describes in detail the application of the principles of the invention to the problems arising out of change of moisture content but clearly the problems arising out of other changes can be solved in similar manner.

The invention is of course not limited to any of the specific details of the embodiment or embodiments particularly described. For example, the closed loop part of the control mechanism may be arranged to operate through a switch rather than a transducer, and most of the parts of the additional means could be replaced by equivalents of one kind or another. The invention, furthermore, can be applied to machines other than scutchers, for example, lap forming machines.

We claim:

1. A control. mechanism in, or for use in, a machine by which the mass per unit length of a traveling material is continuously modified, and comprising. in combination first material thickness sensing means located. at a point just prior to the commencement of said modification and where the width of the material is substantially constant, means for governing compensatively the rate at which material is fed into the machine in response to variations in thickness detected by said first material thickness sensing means and on the basis that the thickness is directly proportional to the mass per unit length, second material thickness sensing means located at a point just after completion of said modification and where the width of the material is substantially constant, means for adjusting said means for governing the rate at which material is fed into the machine compensatively at a rate directly proportional to deviations from a desired thickness sensed by said second material thickness sensing means and also on the basis that the thickness is directly proportional to the mass per unit length, means for detecting changes in the moisture content of the material and for adjusting said second material thickness sensing means compensatively so that in spite of said changes and consequent changes in the relationship between the thickness and the mass per unit length of the material the mass per unit length of the modified material in maintained substantially constant.

2. In a scutcher having a feed lattice, a feed roller, a heater, cages, calender rollers and lap rollers, a control mechanism comprising in combination a first lever system sensitive to variationsin the thickness of fibrous" textile material entering the scutcher between said lever system and said feed roller, a pedal assembly in said first lever system, an adjustable pivotal support for said pedal assembly, drive means for said feed lattice and said feed roller, the speed of said drive means being adapted to be varied compensatively by movement of said pedal assembly which is proportional to said variations in thickness, a second lever system sensitive to deviations from a. predetermined value of the thickness of said material passing through said calender rollers, transducer means operated by said second lever system for converting the sensed deviations into an electrical signal proportional thereto, an amplifier for said signal, a motor driven at a speed proportional to said signal, shiftable means mounting said adjustable pivotable support and driven by said motor for compensatively adjusting said first lever system according to the deviations sensed by said second lever system, a support for said transducer means, screw means for adjusting said support for said transducer means and thereby its setting relative to said second lever system, an electrical bridge, one arm of said bridge accommodating material passing through said calender rollers in such a way that the resistance of said arm varies as a result of changes in the moisture content of the material passing through said calender rollers, another arm of said bridge including a non-linear vari-a ble resistance the characteristics of which are selected according to the effect of said changes in moisture content on the material thickness-mass per unit length relationship, a source of electric power associated with said bridge and modulated thereby in correspondence with the sense and magnitude of any out of balance of said two arms caused by deviation of said moisture content from a predetermined value, a movable contact of said variable resistance, screw means for adjusting the position of said movable contact, and a motor driving both of the said screw means and powered by said source of electric power whereby to bring about a compensatory adjustment of the transducer means setting on such change in moisture content and also to rebalance said bridge.

' 3. A control mechanism in, or for use in, a machine by which a certain property of a traveling material is modified, comprising in combination;

(a) first means for sensing variations in another property of the material 'before modification commences and for governing the action of the machine compensatively according to the sensed variations, said other property being one which, when all properties save said certain property and said other property remain constant, has a given proportionality to said certain property,

(b) second means for sensing variations in said other property of the material after modification is complete,

(c) feed-back means between said second means and said first means for adjusting the action of said first means compensatively according to the variations sensed by said second means, and

(d) third means for sensing changes in a property affecting the proportionality between said certain property and said other property and for adjusting said second means compensatively.

References Cited by the Examiner UNITED STATES PATENTS 278,488 5/1883 Ayers 19-241 2,361,217 10/1944 Lewis 19-240 2,542,3 31 2/ 1951 Hiensch 19-240 2,805,449 9/1957 Martin 19240 2,981,986 5/1961 Neil 19240 3,013,313 12/1961 Catling et al. 19-161 X 3,109,204 11/1963 Linnert et al 19-241 FOREIGN PATENTS 1,237,428 6/ 1960 France.

720,200 4/ 1942 Germany. 284,356 1l/ 1952 Switzerland.

DONALD W. PARKER, Primary Examiner. 

1. A CONTROL MECHANISM IN, OR FOR USE IN, A MACHINE BY WHICH THE MASS PER UNIT LENGTH OF A TRAVELING MATERIAL IS CONTINUOUSLY MODIFIED, AND COMPRISING IN COMBINATION FIRST MATERIAL THICKNESS SENSING MEANS LOCATED AT A POINT JUST PRIOR TO THE COMMENCEMENT OF SAID MODIFICATION AND WHERE THE WIDTH OF THE MATERIAL IS SUBSTANTIALLY CONSTANT, MEANS FOR GOVERNING COMPENSATIVELY THE RATE AT WHICH MATERIAL IS FED INTO THE MACHINE IN RESPONSE TO VARIATIONS IN THICKNESS DETECTED BY SAID FIRST MATERIAL THICKNESS SENSING MEANS AND ON THE BASES THAT THE THICKNESS IS DIRECTLY PROPORTIONAL TO THE MASS PER UNIT LENGTH, SECOND MATERIAL THICKNESS SENSING MENS LOCATED AT A POINT JUST AFTER COMPLETION OF SAID MODIFICATION AND WHERE THE WIDTH OF THE MATERIAL IS SUBSTANTIALLY CONSTANT, MEANS FOR ADJUSTING SAID MEANS FOR GOVERNING THE RATE AT WHICH MATERIAL IS FET INTO THE MAVHINE COMPENSATIVELY AT A RATE DIRECTLY PROPORTIONAL TO DEVIATIONS FROM A DESIRED THICKNESS SENSED BY SAID SECOND MATERIAL THICKNESS SENSING MEANS AND ALSO ON THE BASIS THAT THE THICKNESS IS DIRECTLY PROPORTIONAL TO THE MASS PER UNIT LENGTH, MEANS FOR DETECTING CHANGES IN THE MOISTURE CONTENT OF THE MATERIAL AND FOR ADJUSTING SAID SECOND MATERIAL THICKNESS SENSING MENS COMPENSATIVELY SO THAT IN SPITE OF SAID CHANGES AND CONSQUENT CHANGES IN THE RELATIONSHIP BETWEEN THE THICKNESS AND THE MASS PER UNIT LENGTH OF THE MATERIAL THE MASS PER UNIT LENGTH OF THE MODIFIED MATERIAL IN MAINTAINED SUBSTANTIALLY CONSTANT. 